Crossbar molecular electronic devices (CMED) typically consist of a top and bottom electrode, between which a layer of organic molecules is sandwiched in a planar configuration on an insulating substrate. The particular chemical and electronic properties of an organic molecule define the functionality of the CMED and to date, arrays of such devices have been made demonstrating programmable resistor logic, diode logic, and bistable switching, depending on the choice of the respective molecule.
One challenge with the construction of CMEDs is the fabrication of the top conducting electrode onto the molecular layer. The material for this electrode (usually a metal) is conventionally deposited by thermal or sputter deposition sources positioned with a line-of-sight to the substrate bearing the bottom electrode/molecular layer array. The problem with such sources is that they impart a high kinetic energy to the metal atoms, allowing them to either penetrate the molecular layer and short the device and/or undergo chemical reaction with the organic layer that unpredictably changes its chemical and electronic properties.
One approach to addressing this problem involves chilling the substrate bearing the bottom electrode/molecular layer array in a chamber filled with sub-Torr pressures of an inert gas to moderate the kinetic energies of incoming metal atoms that would originate from sources that do not have a direct line of sight to the substrate. Such an approach, while effective, can be inefficient, time-consuming, and costly, as most of the top electrode source material is wasted.
Thus, there remains a need for a mechanism for protecting the molecular layer during fabrication of the top electrode.